Optical measurement systems typically employ one or more photodetectors to detect incident light and then use information derived from the detected light for various purposes. For example, a photodetector incorporated into a digital camera (in the form of an image sensor) can be used to measure light intensities associated with various objects in a scene to be captured by the digital camera. Digital cameras generally include various exposure settings that can be used to address various ambient lighting conditions. The exposure settings can be suitably adjusted after an initial measurement of ambient light is carried out. The initial measurement may be carried out either by using circuitry contained in the digital camera itself or by using an external light meter. However, such ambient light measurements often prove to be rough approximations that do not accurately reflect the actual amount of ambient light that may be present at a particular moment in time when the camera is used to capture an image of an object located at a distance far from the camera.
In some applications other than photography, ambient light measurements can be carried out using various other techniques and procedures. However, in many instances, even the use of these other techniques and procedures fails to provide satisfactory results. For example, ambient light measurement circuitry used in some traditional time-of-flight optical distance measurement systems for measuring ambient light and addressing resulting adverse effects often proves inadequate and less than optimal. This shortcoming may be attributable, at least in part, to the more complex nature of the distance measurement procedure in comparison to various light detection procedures employed in digital cameras, for example.
As is known, a time-of-flight optical distance measurement system operates by transmitting a beam of light towards a target object and then waiting to receive a reflected portion of the emitted light after reflection by the target object. The time delay between transmission of the light beam and receiving of the reflected light is used to calculate the distance between the measurement system and the target object. Understandably, the amount of reflected light can be very small in comparison to the amount of ambient light that may be present in the vicinity of the optical distance measurement system. Existing optical distance measurement systems attempt to eliminate the effects of the ambient light with limited success primarily due to complexities related to determining an optimal length of time (sampling period) that can be used for detecting an amount of ambient light with a satisfactory level of accuracy. An excessively long sampling period can lead to undesirable measurement delays with no guarantees that the ambient light will remain unchanged at the moment when the reflected light actually reaches a detector at a later instant in time. On the other hand, a short sampling period can lead to an improper measurement of the ambient light level.
It is therefore desirable to provide an optical measurement system that addresses at least some of the issues associated with traditional optical measurement systems incorporating ambient light measurement circuitry.